This invention relates generally to devices used in rotary drilling operations, and more particularly to devices used to clamp drill casing during coupling and uncoupling of sections of drill casing.
During drilling for wells or holes for foundation pilings, the ground formation sometimes will collapse inwardly causing the drill string to become stuck, or the hole to close after the drill sting is removed. When these conditions occur a pipe, referred to as casing, is used to shore-up the bore hole during and after drilling to keep the hole open. A common type of casing uses threaded ends and large pipe couplings to join sections together. When making (coupling together) these joints, if the ground has not collapsed sufficiently around the lower section, the casing will remain free to rotate, not allowing the upper casing portion of the joint to become tightened by rotation into the coupling. The reverse is also true when attempting to break joints (uncouple), the ground will not hold the casing from turning, and allow the joint to be unscrewed, which is required to remove casing sections.
A current solution to this problem is to use a device call slips. This consist of wedges that fit into tapered ways in the drill bushing. Although slips can work well, they can be cumbersome and time consuming to use. They must be driven into place in the tapered ways until they can grip the casing. This system is dependent on a down pressure supplied by the casing weight to develop its grip of the casing. For removal of the slips it is necessary to lift the casing. Slips commonly become stuck and not easily removed.
The foregoing illustrates limitations known to exist in present drill casing grippers. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.